@tuomaz the DDR training is different for every board, it can train a little bit differently even for each boot of the device. It depends on the DDR chips (each DDR chip can be a little bit different internally), on how they are soldered onto the board, on the traces of each PCB.
Could you please try switching branch to hbl with switch-branch hbl? After this wait some time (like 15 minutes) because it schedules a pkgupdate to update all packages. If you already are on the hbl branch, just do a pkgupdate.
Afterwards, install the omnia-uboot packages with opkg install omnia-uboot. Chech whether you have the newest version, with md5sum /usr/share/omnia/uboot-devel. It should print the checksum e2cb89f4a975952073e71beba2b5fa18.
If this checksum is correct, do a nor-update -d to update U-Boot. The new U-Boot supports old DDR training, you can select it from TurrisOS with
fw_setenv omnia_ddr3_training old
reboot
Alternatively, if you have serial connection available to the board, you can also reboot the board into U-Boot and execute the following commands in U-Boot command line
env set omnia_ddr3_training old
env save
reset
If you have the serial connection, please send the output of U-Boot after doing this.